1. Field of the Invention
This invention relates to printers and, more particularly, to an apparatus for curling materials, such as paper, used in such printers.
2. Description of the Related Art
Many materials, such as paper, become curled after bending and/or heating. Paper may also become curled after one side of the paper undergoes a printing process. Electrophotographic imaging (i.e., laser printing) typically involves bonding toner to a sheet of paper using heat. This application of heat, or "fusing," often results in significant curling of the paper. This curling can cause problems in subsequent processing, such as wrinkled paper and paper jams in a laser printer.
This curling problem is reduced by straightening the paper. The paper is straightened by actually curling the paper in an opposite direction. If, for example, the paper curls toward a printed side of the page, the paper can be straightened by curling the paper toward the blank side. Thus the paper is straightened by actually curling the paper.
This concept, of curling paper to straighten paper, is used in laser printers. After the laser printer heats the toner and bonds an image to the paper, the high heat, as mentioned above, can cause the paper to curl. Laser printers use a curling operation to straighten the paper and to reduce the problems associated with the high heat of the fusing process.
Previous curling operations, however, only compensate for one direction of curl. After the image is formed, for example, light weight paper generally curls toward the unprinted, blank side of the paper. Heavy weight paper, on the other hand, generally curls toward the printed side of the paper. Because the printed side of a page is often referred to as the "positive" side, heavy weight paper is said to generally have a "positive" curl after leaving the printing process. Light weight paper curls toward the blank side, so light weight paper is said to generally have a "negative" curl after leaving the printing process. Because previous curling operations are effective for only one direction of curl, they cannot completely straighten the various weights of paper commonly used in a laser printer.
U.S. Pat. No. 5,316,539 to Leemhuis et al., issued May 31, 1994, is an example of these previous curling operations. The apparatus disclosed in this patent is only capable of curling in one direction. Any paper requiring a curling operation in an opposite direction is not adequately straightened, and this paper can cause paper jams and other problems.
There is, accordingly, a need in the art for an apparatus which is capable of curling both positive and negative curled papers.